With more than 50 million individuals affected, the United States is facing a serious challenge in the treatment of hypertension. Oxidative stress is strongly implicated in the pathogenesis of hypertension; however, the role of mitochondrial oxidative stress is not clear. We have found that angiotensin II induces mitochondrial oxidative stress via PKC-dependent activation of NADPH oxidases. This result in activation of mitoKATP channels leading to mitochondrial dysfunction and increase in O27 and H2O2 production by mitochondria. Through a positive feedback loop, the increased mitochondrial H2O2 lead to further activation of cellular NADPH oxidases via c-Scr pathway, resulting in increased cellular O27 production and diminished NO7 bioavailability. This vicious cycle is responsible for overproduction of vascular O27, diminished endothelial NO7 and result in endothelial dysfunction. We suggest that we can interrupt this vicious cycle in endothelial cells by inhibition of mitochondrial oxidative stress using mitochondria-targeted antioxidants. Indeed, treatment of endothelial cells with mitochondria- targeted SOD mimetic mitoTEMPO or inhibition of mitoKATP channels reduced mitochondrial oxidative stress, improved mitochondrial respiration, blocked AngII-induced endothelial oxidative stress and restored NO7. This proposal will investigate the upstream and downstream cellular regulations of mitochondrial ROS. We will examine the role of NOX by depletion or overexpression of specific NOX isoforms using siRNA and transfection techniques. The role of mitochondrial PKC5 in stimulation of mitoKATP dependent production of mitochondrial ROS will be examined. The downstream effect of mitochondrial ROS in redox regulation of c-Src dependent activation of NADPH oxidase will be studied using constitutively active mutant c-Src Y527F. In this proposal we will examine the role of mitochondrial impairment in endothelial dysfunction. Our preliminary data showed that overexpression of mitochondrial superoxide dismutase (SOD2) inhibited AngII-induced endothelial oxidative stress and restored NO7. We suggest that a cross-talk between mitochondrial dysfunction and mitochondrial oxidative stress may constitute a mitochondrial impairment, which drives endothelial dysfunction. In this proposal we will study the effect of mitoTEMPO, SOD2 depletion or overexpression on mitochondrial and endothelial functions. Finally, we will investigate the role of mitochondrial ROS in Ang II - and DOCA-salt induced hypertension using C57Blk/6, tgSOD2 and SOD2() mice. For the first time we have found that treatment of hypertensive animals with mitoTEMPO significantly reduced vascular oxidative stress, increased NO7, improved endothelial dependent relaxation and attenuated hypertension, while the same dose of non-targeted antioxidant TEMPOL did not. The overall objective of this proposal is to gain a clear understanding of the role of mitochondrial oxidative stress in endothelial dysfunction and hypertension, which may provide critical information for the development of new mitochondria-targeted therapeutic agents to treat hypertension.